1. Technical Field
This invention relates to signal monitoring systems in general, and in particular to signal monitoring systems that include a coupler that shields against electromagnetic interference (EMI).
2. Background Information
Near-infrared spectroscopy (NIRS) is an optical spectrophotometric method that can be used to continuously monitor tissue oxygenation. NIRS is based on the principle that light in the near-infrared range (700 nm to 1,000 nm) can pass easily through skin, bone and other tissues where it encounters hemoglobin located mainly within micro-circulation passages; e.g., capillaries, arterioles, and venuoles. Hemoglobin exposed to light in the near-infrared range has specific absorption spectra that varies depending on its oxidation state; i.e., oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) each act as a distinct chromophore. NIRS involves transmitting near-infrared light at specific different wavelengths, and measuring changes in transmitted or reflected light attenuation. NIRS enables concentration changes of the oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) to be monitored. The ability to continually monitor cerebral oxygenation levels, for example, is particularly valuable for patients who are subject to a condition in which oxygenation levels may be compromised.
NIRS systems have been developed that include at least one NIRS sensor assembly, a base unit, and at least one interface cable for connecting the NIRS sensor assembly to the base unit. Each NIRS sensor assembly typically includes at least one light source and at least one light detector, and is operable to generate a detection light signal that is communicated to the base unit for processing. Detection light signals are sent from each NIRS sensor assembly to the base unit of the NIRS system via an interface cable.
A problem common to all NIRS systems is EMI from external sources. EMI can negatively affect the quality of the detection light signal. These problems are not limited NIRS systems; the same or similar problems exist in other signal monitoring systems. What is needed, therefore, is an improved signal monitoring system directed toward these and other problems.